Why do biz-jets, especially Gulfstreams and Globals, deploy their thrust reversers whilst taxiing out ? And in sometimes too.
It's that you don't see airliners doing this.
Thanks.
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Re: Biz-jet thrust reversers activated whilst taxiing.
Keeps the aircraft from speeding up too much. It’s easier on the brakes.
Re: Biz-jet thrust reversers activated whilst taxiing.
1) I believe they do it to test them.
2) I also think they sometimes use them to slow down taxi to save brakes.
2) I also think they sometimes use them to slow down taxi to save brakes.
Re: Biz-jet thrust reversers activated whilst taxiing.
At my air carrier use of thrust reverser during taxi out is generally prohibited.
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- GalaxyFlyer
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Re: Biz-jet thrust reversers activated whilst taxiing.
Every bizjet is over-powered; even at near gross weight, a Global will leave the blocks at idle or slight push on the throttles. That and most flights are quite light, so speed builds quickly. A cycle is a FCOM checklist item, too.
Re: Biz-jet thrust reversers activated whilst taxiing.
TC957 wrote:you don't see airliners doing this.
TC957, with regard to airliners not using reverse thrust while taxiing, aircraft with underwing mounted engines have a greater potential for Foreign Object Damage (FOD) when using reverse thrust at low speeds, i.e., taxi operations. The probability of FOD is reduced on aircraft where the engines are mounted higher on the fuselage, such as t-tail design.
As Woodreau mentioned above (Reply # 4), some operators prohibit its use. At my company, in the Airbus A320 series, for normal operations, assuming full reverse thrust was used on landing, we are required to begin reducing reverse thrust at 80 knots on landing rollout and be at idle reverse by 60 knots. We are a also prohibited from using reverse thrust during normal taxi operations.
e38
Re: Biz-jet thrust reversers activated whilst taxiing.
fr8mech wrote:Keeps the aircraft from speeding up too much. It’s easier on the brakes.
What fr8mech writes. Cessna Center in MCO, see a whole lot of Cessnas taxing with T/Rs deployed down Alpha,
https://www.youtube.com/watch?v=Z8zqoLN ... l=cpockett
Re: Biz-jet thrust reversers activated whilst taxiing.
N1120A wrote:1) I believe they do it to test them.
2) I also think they sometimes use them to slow down taxi to save brakes.
No need to test them but yes, it is to slow down without using the brakes.
And it is used in airliners which have tail mounted engines.
Re: Biz-jet thrust reversers activated whilst taxiing.
Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.
Re: Biz-jet thrust reversers activated whilst taxiing.
TC957 wrote:Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.
Works the same with most turboprops.
Re: Biz-jet thrust reversers activated whilst taxiing.
TC957 wrote:Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.
Turbomachinery has a certain lowest idle to keep running self sustaining.
That’s why you spin up the core engine with bleed air to a certain extent until fuel can be added to reach a stabilised self sustained engine state.
You want a stable engine on idle power, some margin included. And that happens to create already enough thrust to get the aircraft moving/accelerating.
Not really a problem though in real world.
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- GalaxyFlyer
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Re: Biz-jet thrust reversers activated whilst taxiing.
CRJockey wrote:N1120A wrote:1) I believe they do it to test them.
2) I also think they sometimes use them to slow down taxi to save brakes.
No need to test them but yes, it is to slow down without using the brakes.
And it is used in airliners which have tail mounted engines.
Just looked at the Global FCOMs, cycling the T/Rs is a fist flight of day item on the taxi-out, both the RR-powered 6000/6500 and the GE-powered 7500. Cycle, check for proper EICAS indications and stow.
Also, engines need to idle at sufficient rpm to run 400Hz generators and produce sufficient bleed air to cool the cabin.
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- Starlionblue
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Re: Biz-jet thrust reversers activated whilst taxiing.
TC957 wrote:Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.
Because the engines would stop if the mass flow was much lower than idle.
As CRJockey says, it isn't really a problem in the real world. Unless you're in a crowded area or about to turn, you just let the aircraft accelerate to 30 knots, then brake down to 10-15 knots, and repeat the process.
Re: Biz-jet thrust reversers activated whilst taxiing.
Reminds me of doing a delayed engine start on the 727 with an inoperative APU one day when I was a very new FE
Captain decides to do this while taxiing, I turn the packs off, he increases thrust on #1 to get the required duct pressure but this increases our taxi speed so he puts #2 into reverse to avoid riding the brakes
It all worked out and as stated you can do this on a rear engine configured type without FOD concerns but it was a bit rinky dink that day
Captain decides to do this while taxiing, I turn the packs off, he increases thrust on #1 to get the required duct pressure but this increases our taxi speed so he puts #2 into reverse to avoid riding the brakes
It all worked out and as stated you can do this on a rear engine configured type without FOD concerns but it was a bit rinky dink that day
Re: Biz-jet thrust reversers activated whilst taxiing.
On the 4 engine Lockheed JetStar bizjet it was a checklist item to test the thrust reversers by deploying them while taxing out to the runway on the first flight of the day. At home base we would normally use a start cart and start all 4 of the engines, but at out stations we would only start engines #2 and# 3 off of the batteries and let the batteries recharge during taxi and then start #1 and #4 so we would stop the taxi checklist at that point where we would test the reversers.
We could have tested all 4 of the reversers without engines #1 and #4 running because the reversers were hydraulically powered by the hydraulic pump on engine #2. Engine #3 had the backup hydraulic pump, but it didn’t supply hydraulic pressure to the reversers, the thrust reverser backup was the stand by electric hydraulic pump which also could be used on the ground without the engines running to deploy the reversers during maintenance.
We never used the reversers to slow the airplane down while taxiing, even with all 4 engines running, just tapped the brakes every so often to slow the airplane down.
JetStar
We could have tested all 4 of the reversers without engines #1 and #4 running because the reversers were hydraulically powered by the hydraulic pump on engine #2. Engine #3 had the backup hydraulic pump, but it didn’t supply hydraulic pressure to the reversers, the thrust reverser backup was the stand by electric hydraulic pump which also could be used on the ground without the engines running to deploy the reversers during maintenance.
We never used the reversers to slow the airplane down while taxiing, even with all 4 engines running, just tapped the brakes every so often to slow the airplane down.
JetStar
Re: Biz-jet thrust reversers activated whilst taxiing.
Used it all the time taxing the CRJ around. Just don’t exceed reverse idle. It does make a big difference on managing taxi speeds without riding and warming the brakes.
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Re: Biz-jet thrust reversers activated whilst taxiing.
TC957 wrote:Why do biz-jets, especially Gulfstreams and Globals, deploy their thrust reversers whilst taxiing out ? And in sometimes too.
It's that you don't see airliners doing this.
Thanks.
Watching the IL-62 land is quite a sight, deploying the thrust reversers BEFORE touchdown......
https://www.youtube.com/watch?v=N29ZFnQ ... =RyanBomar
MD-80, wheels spooled up during bounce
https://www.youtube.com/watch?v=3mzzt-t ... JustPlanes
TU-154
https://www.youtube.com/watch?v=gybeXt_ ... rgospotter
Re: Biz-jet thrust reversers activated whilst taxiing.
Flying both the G-IV and G-V checking the TRs is a first flight of the day item (as someone mentioned above). We also use them to reduce brakewear. Engine parts are paid for on programs that do not discourage TR use, while brakes are exceptionally expensive to replace.
Re: Biz-jet thrust reversers activated whilst taxiing.
sadde wrote:Flying both the G-IV and G-V checking the TRs is a first flight of the day item (as someone mentioned above). We also use them to reduce brakewear. Engine parts are paid for on programs that do not discourage TR use, while brakes are exceptionally expensive to replace.
Thanks for your input , Sadde. So whats the cost for a full set of new brakes then on something like a G550 ? And on average useage, how long does a set last ?
Re: Biz-jet thrust reversers activated whilst taxiing.
65-90k per brake from what I can remember, two per main gear. So, about 350k for an entirely new set. Depending on wear and tear/ pilot taxiing habits I see us replacing a single brake about every 7-8 months on average. They do not wear evenly, so it’s unusual to replace more than one at a time
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- GalaxyFlyer
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Re: Biz-jet thrust reversers activated whilst taxiing.
I know of Globals and Challengers have gone years between brake replacements, even a decade at 400 hours per year flying, tho.
Re: Biz-jet thrust reversers activated whilst taxiing.
We're on year 13 with our Global and still the original brakes. 4000+TT with 1500+ cycles. The brakes on a Global are VERY robust. A new set of brakes are in the $100's of Thousands.
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- GalaxyFlyer
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Re: Biz-jet thrust reversers activated whilst taxiing.
26point2 wrote:We're on year 13 with our Global and still the original brakes. 4000+TT with 1500+ cycles. The brakes on a Global are VERY robust. A new set of brakes are in the $100's of Thousands.
I didn’t want to brag, but if he’s changing brakes on a Gulfstream every 9 months, something’s wrong.
Re: Biz-jet thrust reversers activated whilst taxiing.
I remember in 1980 my chief pilot complaining to me about the $1700.00 it cost to overhaul a brake assembly on the Lockheed JetStar. They were the old fashioned multiple disc steel brakes and would last about 400 to 500 landings, I told him if he wanted to extend the life of the brakes, quit the heavy use of the brakes trying to make the first turnoff on the runway when slowed down enough after the thrust reversers were stowed, let the airplane roll to the next turnoff and go easy on the brakes. On RCA Corporation's JetStar, also based at HPN they had that policy and were getting 1200 landings on their brakes.
Of course that went in one ear and out the other.
On my other chief of maintenance job on the JetStar, we were getting 300 or so landings on the left side brakes and about 450 landings on the right side. He was a very active tennis player and I guess his left leg was more stronger than his right leg and when applying the brakes, either when landing or taxiing he unconsciously applied more pressure on his left leg than his right and caused more wear on the left side. When I told him what I thought about the cause of the left side wearing out faster than the right side, he blamed it on the overhauls, so again in one ear and out the other.
Ah, the joys of being a corporate flight department chief of maintenance and answering to chief pilots who were complete idiots.
JetStar
Of course that went in one ear and out the other.
On my other chief of maintenance job on the JetStar, we were getting 300 or so landings on the left side brakes and about 450 landings on the right side. He was a very active tennis player and I guess his left leg was more stronger than his right leg and when applying the brakes, either when landing or taxiing he unconsciously applied more pressure on his left leg than his right and caused more wear on the left side. When I told him what I thought about the cause of the left side wearing out faster than the right side, he blamed it on the overhauls, so again in one ear and out the other.
Ah, the joys of being a corporate flight department chief of maintenance and answering to chief pilots who were complete idiots.
JetStar
Re: Biz-jet thrust reversers activated whilst taxiing.
GalaxyFlyer wrote:26point2 wrote:We're on year 13 with our Global and still the original brakes. 4000+TT with 1500+ cycles. The brakes on a Global are VERY robust. A new set of brakes are in the $100's of Thousands.
I didn’t want to brag, but if he’s changing brakes on a Gulfstream every 9 months, something’s wrong.
Floating fleet baby! I completely agree.
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